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Quick OTL / transformer coupled question

post #1 of 21
11/2/09 at 10:29pm
Thread Starter 
I've been reading about amps and have picked up that, all else equal, OTL amps favor high impedance headphones and transformer coupled amps favor low impedance headphones. That may be an oversimplification, but good enough for my purposes.

My question is, is this information only relevant for tube amps? None of my reading about SS amps seems to turn up these terms and I'm figuring it must be because those are tube-only terms.

When looking for a SS amp for low impedance headphones, do I just need to find one with some sort of gain settings?

Thanks.
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post #2 of 21
11/2/09 at 10:59pm
Transformers don't "favor" low impedance headphones - transformers have winding impedance and should be matched to the impedance of the headphones or if not possible (and most manufacturers won't say this), in the worst case, at least lower than impedance of headphones.

OTL also does not "favor" high impedance, most tubes simply suck at driving low impedance.

Most opamps or transistor amps are designed to have output impedance of nearly 0 so impedance mismatch is not a problem.
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post #3 of 21
11/2/09 at 11:09pm
Thread Starter 
Okay but you know what I'm getting at. It's why people with Grados are recommended to get a WA6 instead of a WA3.

Thanks for answering my question, though.
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post #4 of 21
11/3/09 at 3:30am
Hi it is certainly possible to have a transformer coupled output in a solid state design....my 1979 Sony tv has an output tx as did an early seventies Akai stereo receiver (45wpc discrete)
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post #5 of 21
11/3/09 at 8:28pm
Right - ONE issue is really the output impedance of the amp versus the impedance of the headphones - some (if not most) OTL tube amps have an output impedance that will be higher than a headphone like the Grados, and that's not ideal.

Further, many tube amps have the ability to swing a lot of voltage, which high impedance headphones need, but are less good at swinging a lot of current, which low impedance headphones need.
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post #6 of 21
11/3/09 at 9:06pm
Quote:
Originally Posted by Skylab View Post
Right - ONE issue is really the output impedance of the amp versus the impedance of the headphones - some (if not most) OTL tube amps have an output impedance that will be higher than a headphone like the Grados, and that's not ideal.

Further, many tube amps have the ability to swing a lot of voltage, which high impedance headphones need, but are less good at swinging a lot of current, which low impedance headphones need.
Yeah, that's one advantage that a transformer output amp can have. Because the OPT will be a step-down, you can generally get a lower output impedance compared to an OTL, and with the right taps, you can deliver the same power to both high and low impedance 'phones.

Here's Gary Dahl's Espressivo headphone amp that takes advantage of the Peerless TL-404 autoformer which was specifically designed for driving headphones.

Espressivo Amplifier

se
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post #7 of 21
11/5/09 at 3:48am
Quote:
Originally Posted by Skylab View Post
Right - ONE issue is really the output impedance of the amp versus the impedance of the headphones - some (if not most) OTL tube amps have an output impedance that will be higher than a headphone like the Grados, and that's not ideal.

Further, many tube amps have the ability to swing a lot of voltage, which high impedance headphones need, but are less good at swinging a lot of current, which low impedance headphones need.
I had send a step down/up transformers headphone coveter to you. It may be will arrive your hand soon. It can matching with most high impeadance Headphone amps to drive low impedance Cans. It also can work in reverse mode , stepup voltage to drive high impedance Cans.
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post #8 of 21
11/5/09 at 10:36am
Thanks Joe! Looking forward to trying that out!
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post #9 of 21
11/5/09 at 1:27pm
Quote:
Originally Posted by Hz_joe View Post
I had send a step down/up transformers headphone coveter to you. It may be will arrive your hand soon. It can matching with most high impeadance Headphone amps to drive low impedance Cans. It also can work in reverse mode , stepup voltage to drive high impedance Cans.
Can you give more details on this? What are the turns ratios and winding resistances?

Thanks.

se
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post #10 of 21
11/5/09 at 2:13pm
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Can you give more details on this? What are the turns ratios and winding resistances?

Thanks.

se
4:1
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post #11 of 21
11/5/09 at 2:31pm
Quote:
Originally Posted by Hz_joe View Post
4:1
Thanks.

No winding resistance info?

se
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post #12 of 21
11/6/09 at 4:16am
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Thanks.

No winding resistance info?

se

Winding resistance is not criticle factor ! Most headphone no need high damping factor ! Especially on Full enclose type. Too much damping sound may be not good !
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post #13 of 21
11/6/09 at 4:40am
Quote:
Originally Posted by Hz_joe View Post
Winding resistance is not criticle factor ! Most headphone no need high damping factor ! Especially on Full enclose type. Too much damping sound may be not good !
But many people feel source impedance is critical and not everyone wants to drive their headphones from a source with too high an output impedance. Knowing the winding resistances would allow people to better assess whether or not they want to go with a transformer option, especially when used as a step-up where the primary winding resistance will be multiplied by a factor of 16.

That could be quite significant depending on what the winding resistance is.

se
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post #14 of 21
11/6/09 at 4:55am
Quote:
Originally Posted by Koyaan I. Sqatsi View Post
But many people feel source impedance is critical and not everyone wants to drive their headphones from a source with too high an output impedance. Knowing the winding resistances would allow people to better assess whether or not they want to go with a transformer option, especially when used as a step-up where the primary winding resistance will be multiplied by a factor of 16.

That could be quite significant depending on what the winding resistance is.

se
Winding resistance not 16! multiplied by a factor of 16 is AC impedance. May be you can found Hints on commercial products. It series a 100 Ohm or high resistor at output, Why ?
It only a Prototype , Still need some fine adjust. More detail data will be post later.
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post #15 of 21
11/6/09 at 1:25pm
Very interesting thread!

By sure OTL's, usually, improve their performances proportionally with the increase of the headphone's impedance.
@ Hz_joe
Then the amplifier "see" your transformer like an high impedance "charge", and the output impedance to the headphone is correct? 4:1, it means that the ampli, for example, see a 240Ohms charge and the output is 60OHMs?

Is it possible do the same, or something close, with a resistor?
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